This invention relates to a process for alkylating polycyclic paraffins to form lubricating stocks by contacting the polycyclic paraffin with an alkylating agent in the presence of a zeolite alkylation catalyst.
Diamondoid compounds exemplify the polycyclic alkanes useful in the present process. The term "diamondoid" as used herein refers to a family of compounds including adamantane and its higher homologs such as diamantane and triamantane as well as their substituted derivatives.
While diamondoid compounds may be synthesized in the laboratory, the costs associated with laboratory synthesis have in the past precluded consideration of diamondoid compounds such as adamantane as high volume raw materials. Fortunately, however, a naturally occurring deposit of these compounds has recently been discovered in which the diamondoid compounds are dissolved in natural gas. The production of natural gas is complicated by the presence of these heavy hydrocarbons in the subterranean formation in which the gas is found. Under conditions prevailing in the subterranean reservoirs, the heavy hydrocarbons may be partially dissolved in the compressed gas or finely divided in a liquid phase. The decrease in temperature and pressure attendant to the upward flow of gas as it is produced to the surface result in the separation of solid hydrocarbonaceous material from the gas. This solid material has been found to be rich in diamondoid compounds. Unfortunately, however, the deposition of this solid initially caused severe plugging problems both in the natural gas well and in the downstream production string.
Various processes have been developed to prevent the formation of such precipitates or to remove them once they have formed. These include mechanical removal of the deposits and the batchwise or continuous injection of a suitable solvent. Recovery of one such class of heavy hydrocarbons, i.e. diamondoid materials, from natural gas is detailed in commonly assigned.
These natural gas streams contain a small proportion of diamondoid compounds, but their considerable volumetric flow provides a sufficient quantity of diamondoids to consider these materials as industrial feedstocks. For a survey of the chemistry of diamondoid compounds, see Fort, Jr., Raymond C., The Chemistry of Diamond Molecules, Marcel Dekker, 1976.
In recent times, new sources of hydrocarbons have been brought into production which, for some unknown reason, have substantially larger concentrations of diamondoid compounds. Whereas in the past, the amount of diamondoid compounds has been too small to cause operational problems such as production cooler plugging, now these compounds represent both a larger problem and a larger opportunity. The presence of diamondoid compounds in natural gas has been found to cause plugging in the process equipment requiring costly maintenance downtime to remove. On the other hand, these very compounds which can deleteriously affect the profitability of natural gas production are themselves valuable products. Specifically, it has been found that such polycyclic alkanes can be catalytically alkylated with certain olefins in the presence of a zeolite catalyst to form useful lubricating stocks.
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic properties for various types of hydrocarbon conversion. Certain zeolitic materials are ordered, porous crystalline aluminosilicates having a definite crystalline structure as determined by X-ray diffraction, within which there are a large number of smaller cavities which may be interconnected by a number of still smaller channels or pores. These cavities and pores are uniform in size within a specific zeolitic material. Since the dimensions of these pores are such as to accept for adsorption molecules of certain dimensions while rejecting those of larger dimensions, these materials have come to be known as "molecular sieves" and are utilized in a variety of ways to take advantage of these properties. Such molecular sieves, both natural and synthetic, include a wide variety of positive ion-containing crystalline silicates. These silicates can be described as a rigid three-dimensional framework of SiO.sub.4 and Periodic Table Group IIIA element oxide, e.g., AlO.sub.4, in which the tetrahedra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total Group IIIA element, e.g., aluminum, and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahedra containing the Group IIIA element, e.g., aluminum, is balanced by the inclusion in the crystal of a cation, e.g., an alkali metal or an alkaline earth metal cation. This can be expressed wherein the ratio of the Group IIIA element, e.g., aluminum, to the number of various cations, such as Ca/2, Sr/2, Na, K or Li, is equal to unity. One type of cation may be exchanged either entirely or partially with another type of cation utilizing ion exchange techniques in a conventional manner. By means of such cation exchange, it has been possible to vary the properties of a given silicate by suitable selection of the cation. The spaces between the tetrahedra are occupied by molecules of water prior to dehydration.
Prior art techniques have resulted in the formation of a great variety of synthetic zeolites. Many of these zeolites have come to be designated by letter or other convenient symbols, as illustrated by zeolite Z (U.S. Pat. No. 2,882,243); zeolite X (U.S. Pat. No. 2,882,244); zeolite Y (U.S. Pat. No. 3,130,007); zeolite ZK-5 (U.S. Pat. No. 3,247,195); zeolite ZK-4 (U.S. Pat. No. 3,314,752); zeolite ZSM-5 (U.S. Patent No. 3,702,886); zeolite ZSM-11 (U.S. Pat. No. 3,709,979); zeolite ZSM-12 (U.S. Pat. No. 3,832,449); zeolite ZSM-20 (U.S. Pat. No. 3,972,983); zeolite ZSM-35 (U.S. Pat. No. 4,016,245); and zeolite ZSM-23 (U.S. Pat. No. 4,076,842), merely to name a few.
The SiO.sub.2 /Al.sub.2 O.sub.3 ratio of a given zeolite is often variable. For example, zeolite X can be synthesized with SiO.sub.2 /Al.sub.2 O.sub.3 ratios of from 2 to 3; zeolite Y, from 3 to about 6. In some zeolites, the upper limit of the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is unbounded. ZSM-5 is one such example wherein the SiO.sub.2 /Al.sub.2 O.sub.3 ratio is at least 5 and up to the limits of present analytical measurement techniques. U.S. Pat. No. 3,941,871 (Re. 29,948) discloses a porous crystalline silicate made from a reaction mixture containing no deliberately added alumina in the recipe and exhibiting the X-ray diffraction pattern characteristic of ZSM-5. U.S. Pat. Nos. 4,061,724; 4,073,865; and 4,104,294 describe crystalline silicates of varying alumina and metal content.
Alkylation is one of the most important and useful reactions of hydrocarbons. Lewis and Bronsted acids, including a variety of natural and synthetic zeolites, have been used as catalysts. Alkylation of aromatic hydrocarbon compounds employing certain crystalline zeolite catalysts is known in the art. For instance, U.S. Pat. No. 3,251,897 describes liquid phase alkylation in the presence of crystalline aluminosilicates such as faujasite, heulandite, clinoptilolite, mordenite, dachiardite, zeolite X and zeolite Y. The temperature of such alkylation procedure does not exceed 600.degree. F., thereby maintaining patentee's preferable operating phase as substantially liquid.
U.S. Pat. No. 2,904,607 shows alkylation of hydrocarbon compounds in the presence of certain crystalline zeolites. The zeolites described for use in this patent are crystalline metallic aluminosilicates, such as, for example, magnesium aluminosilicate.
U.S. Pat. No. 3,173,965 discloses the alkylation of benzene with olefin in the presence of a Friedel-Crafts catalyst, e.g. AlCl.sub.3, AlBr.sub.3, FeCl.sub.3, SnCl.sub.4, BF.sub.3, ZnCl.sub.2, HF, H.sub.2 SO.sub.4, P.sub.2 O.sub.5 and H.sub.3 PO.sub.4, to provide a polyalkylated benzene product of relatively high viscosity index (V.I.), i.e. from 90 to 245, which is useful as a lubricant.
According to U.S. Pat. No. 4,035,308, excess benzene is alkylated with decene dimer in the presence of BF.sub.3 -promoted anhydrous AlCl.sub.3 to provide a monoalkyl benzene product useful as a lubricant or power transmission fluid.
U.S. Pat. No. 4,148,834 describes a two-step alkylation process for preparing di-long chain alkyl aromatic compounds, useful as lubricants, in which aromatic hydrocarbon is alkylated with linear monoolefin in the presence of HF catalyst in a first step and aluminum chloride or aluminum bromide catalyst in a second step.
U.S. Pat. No. 4,691,068 discloses the preparation of long chain monoalkyl aromatics, useful in producing detergents, employing a Friedel-Crafts catalyst, e.g. AlCl.sub.3 --HCl, and featuring the recycle of a heavy boiling product fraction to the alkylation reaction